Interleukin 2 (IL-2) is a pluripotent cytokine produced primarily by activated CD4+ T cells, which plays a crucial role in producing a normal immune response. IL-2 promotes proliferation and expansion of activated T lymphocytes, potentiates B cell growth, and activates monocytes and natural killer cells. It was by virtue of these activities that IL-2 was tested and is used as an approved treatment of cancer (aldesleukin, Proleukin®).
In eukaryotic cells, human IL-2 is synthesized as a precursor polypeptide of 153 amino acids, from which 20 amino acids are removed to generate mature secreted IL-2 (Taniguchi 1983). Recombinant human IL-2 has been produced in E. coli (Rosenberg 1984), in insect cells (Smith 1985) and in mammalian COS cells (Taniguchi 1983).
Interleukin-2 (IL-2) is a four α-helical bundle type I cytokine first identified as a T cell growth factor (Morgan et al., Science 193: 1007 (1976)) but subsequently shown to have broad actions. IL-2 promotes T helper differentiation (Zhu et al., Annual review of immunology 28: 445 (2010); Liao et al., Nat Immunol 9: 1288 (2008); and Liao et al., Nat Immunol 12: 551 (2011)) and the development of regulatory T (Treg) cells (Cheng et al., Immunol Rev 241: 63 (2011)), induces natural killer and lymphokine activated killer activity (Liao et al., Immunity 38: 13 (2013)), and mediates activation-induced cell death (AICD) (Lenardo et al., Nature 353: 858 (1991)).
IL-2 works by interacting with three different receptors: the interleukin 2 receptor alpha (IL-2Rα; CD25), the interleukin 2 receptor beta (IL-2Rβ; CD122), and the interleukin 2 receptor gamma (IL-2Rγ; CD32; common gamma chain). The first receptor to be identified was the IL-2Rα, which is a 55 kD polypeptide (p55) that appears upon T cell activation and was originally called Tac (for T activation) antigen. The IL-2Rα binds IL-2 with a Kd of approximately 10−8 M, and is also known as the “low affinity” IL-2 receptor. Binding of IL-2 to cells expressing only the IL-2Rα does not lead to any detectable biologic response.
IL-2 signals via intermediate affinity receptors (Kd˜10−9 M) on resting T cells and NK cells that consist of IL-2Rβ and the common cytokine receptor γ chain, γc (IL-2Rγ), or via high affinity receptors (Kd˜10−11 M) on activated lymphocytes and Treg cells, which additionally express IL-2Rα (CD25) (Lenardo et al., Nature 353: 858 (1991); and Yuan et al., Immunol Rev 259: 103 (2014)). Whereas γc is shared by the receptors for IL-4, IL-7, IL-9, IL-15, and IL-21 (Leonard et al., Nature Reviews Immunology 1: 200 (2001)) and encoded by the gene mutated in humans with X-linked severe combined immunodeficiency (Noguchi et al., Cell 73: 147 (Apr. 9, 1993)), IL-2Rβ is shared by the receptor for IL-15 (Waldmann, Nature Reviews Immunology 6: 595 (2006)), a cytokine that is critical for normal development of NK cells and memory CD8+ T cells (Waldmann, Nature Reviews Immunology 6: 595 (2006)).
The three dimensional structures of IL-2 and IL-15 bound to their receptors provide insights into receptor assembly and signaling (Wang et al., Science 310: 1159 (2005); and Ring et al., Nat Immunol 13: 1187 (2012)). In addition to their physiological roles in the normal immune response, IL-2 and IL-15 can promote pathologic responses, and a therapeutic goal is to maintain desired actions of these cytokines while blocking untoward autoimmune or immunosuppressive responses. Two monoclonal antibodies (mAbs) to human IL-2Rα, Daclizumab and Basiliximab, are approved by the FDA and exhibit efficacy in renal transplantation rejection (Vincenti et al., N Engl J Med 338: 161 (1998)), cardiac transplantation (Hershberger et al., N Engl J Med 352: 2705 (2005)), multiple sclerosis (Gold et al., Lancet 381: 2167 (2013)), and asthma (Bielekova et al., Proc Natl Acad Sci USA 101: 8705 (2004); and Busse et al., Am J Respir Crit Care Med 178: 1002 (2008)) but they do not block IL-2 signaling via intermediate affinity IL-2Rβ-γc receptors expressed on NK and memory CD8+ cells and cannot block IL-15 signaling (Tkaczuk et al., Am J Transplant 2: 31 (2002)). Although anti-human IL-2Rβ mAb Mikβ1 can block trans-presentation of IL-2 and IL-15 to cells expressing IL-2Rβ-γc receptors (Morris et al., Proc Natl Acad Sci USA 103: 401 (2006)), it is relatively ineffective in blocking cis-signaling by IL-2 or IL-15 via their high affinity heterotrimeric receptor complexes (Morris et al., Proc Natl Acad Sci USA 103: 401 (2006); and Waldmann et al., Blood 121: 476 (2013)). As such, new IL-2 muteins that can block one or more IL-2 and/or IL-15 functions are needed. The present disclosure provides novel IL-2 muteins that function as IL-2 partial agonists and antagonists.